Merge new string builtin

This adds the new builtin 'string' which supports various string
manipulation and matching algorithms, including PCRE based regular
expressions.

Fixes #2296

Squashed commit of the following:

commit 4c3eaeb6e57d76463e9683c327142b0aeafb92b8
Author: ridiculousfish <corydoras@ridiculousfish.com>
Date:   Sat Sep 12 12:51:30 2015 -0700

    Remove testdata and doc dirs from pcre2 source

commit b2a8b4b50f2398b204fb72cfe4b5ba77ece2e1ab
Merge: 11c8a47 7974aab
Author: ridiculousfish <corydoras@ridiculousfish.com>
Date:   Sat Sep 12 12:32:40 2015 -0700

    Merge branch 'string' of git://github.com/msteed/fish-shell into string-test

commit 7974aab6d367f999f1140ab34c2535cef5cf3b00
Author: Michael Steed <msteed@saltstack.com>
Date:   Fri Sep 11 13:00:02 2015 -0600

    build pcre2 lib only, no docs

commit eb20b43d2d96b7e6d24618158ce71078de83c40b
Merge: 1a09e70 5f519cb
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 20:00:47 2015 -0600

    Merge branch 'string' of github.com:msteed/fish-shell into string

commit 1a09e709d028393c9e9e6dc9a84278f399a15f3d
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 19:58:24 2015 -0600

    rebase on master & address the fallout

commit a0ec9772cd1a0a548a501a7633be05dab4e5ee46
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 19:26:45 2015 -0600

    use fish's wildcard_match() for glob matching

commit 64c25a01e3f7234f220ba13545cf658a7492b1a4
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 27 08:19:23 2015 -0600

    some fixes from review

    - string_get_arg_stdin(): simplify and don't discard the argument when
      the trailing newline is absent
    - fix calls to pcre2 for e.g. string match -r -a 'a*' 'b'
    - correct test for args coming from stdin

commit ece7f35ec5f4093763627d68d671b6c0c876896d
Author: Michael Steed <msteed68@gmail.com>
Date:   Sat Aug 22 19:35:56 2015 -0600

    fixes from review

    - Makefile.in: restore iwyu target
    - regex_replacer_t::replace_matches(): correct size passed to realloc()

commit 9ff7477a926c4572e26171cab3cd42f8086be678
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 20 13:08:33 2015 -0600

    Minor doc improvements

commit baf4e096b22dde3063b85b833795eb570d660ba7
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:29:02 2015 -0600

    another attempt to fix the ci build

commit 896a2c2b279a419747bea26102229fbe84534a6f
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:03:49 2015 -0600

    Updates after review comments

    - make match/replace without -a operate on the first match on each
      argument
    - use different exit codes for "no operation performed" and errors, as
      grep does
    - refactor regex compile code
    - use human-friendly error messages from pcre2
    - improve error handling & reporting elsewhere
    - add a few tests
    - make some doc fixes
    - some simplification & cleanup
    - fix ci build failure (I hope)

commit efd47dcbda2ca247d58bee56a7774cd75a1062fd
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 12 00:26:07 2015 -0600

    fix dependencies for parallel make

commit ed0850e2db467362066a3d94e3ececd17c1756cd
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 23:37:22 2015 -0600

    Add missing pcre2 files + .gitignore

commit 9492e7a7e929c03554336be1ddf80ca6b37f53c5
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:44:05 2015 -0600

    add pcre2-10.20 and update license.hdr

commit 1a60b933718feb20c0bf7c9e257b8e495014ea1b
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:41:19 2015 -0600

    add string builtin files

    - string builtin source, tests, & docs
    - changes to configure.ac & Makefile.in

commit 5f519cb2a2c05213e0a88a7add7af288bc1c1352
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Sep 10 19:26:45 2015 -0600

    use fish's wildcard_match() for glob matching

commit 2ecd24f79500879e2de5bdf1b4c19dd44fc6ac85
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 27 08:19:23 2015 -0600

    some fixes from review

    - string_get_arg_stdin(): simplify and don't discard the argument when
      the trailing newline is absent
    - fix calls to pcre2 for e.g. string match -r -a 'a*' 'b'
    - correct test for args coming from stdin

commit 45b777e4dc85c05cd4a186f4bdcae543c21aaf08
Author: Michael Steed <msteed68@gmail.com>
Date:   Sat Aug 22 19:35:56 2015 -0600

    fixes from review

    - Makefile.in: restore iwyu target
    - regex_replacer_t::replace_matches(): correct size passed to realloc()

commit 981cbb6ddf742a5fe8881af916e7b870b7e6422a
Author: Michael Steed <msteed68@gmail.com>
Date:   Thu Aug 20 13:08:33 2015 -0600

    Minor doc improvements

commit ddb6a2a8fdb6aa31aad41e80d5481bb32c6ed8ff
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:29:02 2015 -0600

    another attempt to fix the ci build

commit 1e34e3191b028162863d263e9868052f75194aa5
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 19 18:03:49 2015 -0600

    Updates after review comments

    - make match/replace without -a operate on the first match on each
      argument
    - use different exit codes for "no operation performed" and errors, as
      grep does
    - refactor regex compile code
    - use human-friendly error messages from pcre2
    - improve error handling & reporting elsewhere
    - add a few tests
    - make some doc fixes
    - some simplification & cleanup
    - fix ci build failure (I hope)

commit 34232e152df17a3cfbf0a094dd51d148a4f04e6f
Author: Michael Steed <msteed68@gmail.com>
Date:   Wed Aug 12 00:26:07 2015 -0600

    fix dependencies for parallel make

commit 00d7e781697f53454beb91c1d0fc4b2d28d6e034
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 23:37:22 2015 -0600

    Add missing pcre2 files + .gitignore

commit 4498aa5f576e09634f7f619443e74d2f33c108e4
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:44:05 2015 -0600

    add pcre2-10.20 and update license.hdr

commit 290c58c72e22db644ccf6fa9088051644980ed0a
Author: Michael Steed <msteed68@gmail.com>
Date:   Tue Aug 11 22:41:19 2015 -0600

    add string builtin files

    - string builtin source, tests, & docs
    - changes to configure.ac & Makefile.in

1 files changed, 121 insertions, 0 deletions

diff --git a/pcre2-10.20/pcre2-config.in b/pcre2-10.20/pcre2-config.in
new file mode 100644
index 00000000..932160ef
--- /dev/null
+++ b/pcre2-10.20/pcre2-config.in
@@ -0,0 +1,121 @@
+#!/bin/sh
+
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+exec_prefix_set=no
+
+cflags="[--cflags]"
+libs=
+
+if test @enable_pcre2_16@ = yes ; then
+  libs="[--libs16] $libs"
+fi
+
+if test @enable_pcre2_32@ = yes ; then
+  libs="[--libs32] $libs"
+fi
+
+if test @enable_pcre2_8@ = yes ; then
+  libs="[--libs8] [--libs-posix] $libs"
+  cflags="$cflags [--cflags-posix]"
+fi
+
+usage="Usage: pcre2-config [--prefix] [--exec-prefix] [--version] $libs $cflags"
+
+if test $# -eq 0; then
+      echo "${usage}" 1>&2
+      exit 1
+fi
+
+libR=
+case `uname -s` in
+  *SunOS*)
+  libR=" -R@libdir@"
+  ;;
+  *BSD*)
+  libR=" -Wl,-R@libdir@"
+  ;;
+esac
+
+libS=
+if test @libdir@ != /usr/lib ; then
+  libS=-L@libdir@
+fi
+
+while test $# -gt 0; do
+  case "$1" in
+  -*=*) optarg=`echo "$1" | sed 's/[-_a-zA-Z0-9]*=//'` ;;
+  *) optarg= ;;
+  esac
+
+  case $1 in
+    --prefix=*)
+      prefix=$optarg
+      if test $exec_prefix_set = no ; then
+        exec_prefix=$optarg
+      fi
+      ;;
+    --prefix)
+      echo $prefix
+      ;;
+    --exec-prefix=*)
+      exec_prefix=$optarg
+      exec_prefix_set=yes
+      ;;
+    --exec-prefix)
+      echo $exec_prefix
+      ;;
+    --version)
+      echo @PACKAGE_VERSION@
+      ;;
+    --cflags)
+      if test @includedir@ != /usr/include ; then
+        includes=-I@includedir@
+      fi
+      echo $includes @PCRE2_STATIC_CFLAG@
+      ;;
+    --cflags-posix)
+      if test @enable_pcre2_8@ = yes ; then
+        if test @includedir@ != /usr/include ; then
+          includes=-I@includedir@
+        fi
+        echo $includes @PCRE2_STATIC_CFLAG@
+      else
+        echo "${usage}" 1>&2
+      fi
+      ;;
+    --libs-posix)
+      if test @enable_pcre2_8@ = yes ; then
+        echo $libS$libR -lpcre2posix -lpcre2-8
+      else
+        echo "${usage}" 1>&2
+      fi
+      ;;
+    --libs8)
+      if test @enable_pcre2_8@ = yes ; then
+        echo $libS$libR -lpcre2-8
+      else
+        echo "${usage}" 1>&2
+      fi
+      ;;
+    --libs16)
+      if test @enable_pcre2_16@ = yes ; then
+        echo $libS$libR -lpcre2-16
+      else
+        echo "${usage}" 1>&2
+      fi
+      ;;
+    --libs32)
+      if test @enable_pcre2_32@ = yes ; then
+        echo $libS$libR -lpcre2-32
+      else
+        echo "${usage}" 1>&2
+      fi
+      ;;
+    *)
+      echo "${usage}" 1>&2
+      exit 1
+      ;;
+  esac
+  shift
+done